The present invention relates to apparatuses for assembling bicycle frames and, more particularly, apparatuses for assembling bicycle frames having tubular components which are press fitted together.
The typical lightweight bicycle frame comprises a head tube for supporting the handlebars and front fork, a seat post bracket for supporting the bicycle seat, and a bottom bracket which supports the crank assembly and chain stays which, in turn, support the rear wheel. The head tube is connected to the seat post bracket by a cylindrical top tube, and the bottom bracket is connected to the head tube and seat post bracket by a down tube and seat mast, respectively. The resulting structure is substantially triangular in shape and provides a rigid assembly.
Typically, the aforementioned components were connected to each other by welding or brazing, since that type of connection provided the requisite rigidity and strength. However, some frames currently are being constructed in which adhesives are used to connect the components, and in which components not susceptible to brazing are used. Furthermore, brazing the components of a frame together is a time-consuming, and therefore expensive, method of frame assembly.
In one type of frame construction, the head tube, bottom bracket, and seat post bracket each include cylindrical lugs which are sized to telescope within the ends of the connecting tubes to form an interference fit. The lugs are first coated with an adhesive, which is preferably a thermalsetting adhesive, and the head tube, bottom bracket, and seat post bracket are urged toward each other to drive their respective lugs into the ends of the connecting tubes. An example of such a bicycle frame construction is shown and described in detail in U.S. application Ser. No. 677,707, filed Dec. 4, 1984, now U.S. Pat. No. 4,583,755 and assigned to the assignee of the present invention.
It is desirable to size the lugs and tubes of such frames to provide a secure interference fit so that, once assembled, the frame may be stored or transported to a furnace to effect the setting up of the adhesive without the frame components moving out of alignment with each other. Consequently, the forces required to achieve such an interference fit to assemble such frame necessitate the use of power-assisted machinery. However, there do not presently exist machines which are specifically designed for the assembly of such bicycle frames. In order to assemble such frames, other types of jigs or fixtures are adapted to receive a portion of the frame to be constructed. Such fixtures include components for clamping the brackets and head tube, and also include hydraulic cylinder motors for urging the clamping devices together, thereby driving the lugs into the ends of the tube.
A disadvantage with such types of machines is that the assembly of a frame is accomplished iteratively rather than in a continuous process. Since the angular relationships between the connecting tube change as the lugs of the brackets and head tube are forced into the tube ends, the lugs must be forced in incrementally in a series of steps in which the lugs of the seat post bracket, head tube, and bottom bracket are sequentially urged into the tube ends.
Such methods and apparatuses have the disadvantage of assembling a bicycle frame of this type in a time-consuming and labor-intensive manner. Consequently, the frames cannot be constructed in a manner so that the resultant bicycle can be sold at a reasonably competitive price. Accordingly, there is a need for a machine for assembling bicycle frames of the type having lugged brackets and head tubes in which the lugs are forced into the connecting tubes by an interference fit in an efficient and continuous motion. Furthermore, such a machine should have a high rate of output and be designed for the rapid loading and unloading of frame components and finished frames.